Do we know anything about the reaction within the kingdom back home? Was this kind of thing expected and encouraged? For dukes to just unilaterally set themselves up as sovereigns of foreign lands? Did the king of Francia at any point try to say "Wait a minute, England should be mine, since you're just my duke?"
I think you might have misunderstood France in the 11th century. Early Capetian kings were weak, their reach didn't go far beyond Ile-de-France, the Dukes and Counts were basically running autonomous kingdoms doing as they wished, including waging wars against the king of France himself. The French king's symbolic power of being anointed by god didn't have much real currency when no institution could enforce it. The real question to ask is how the French king GAINED in power, not how they lost power when they didn't have much to begin with.
Anyway, William the Conqueror was taking England for himself and held the title independently of France. The conquest didn't unify England and Normandy into a single realm; they were still two separated realms with the same titular head. Similarly, so called Angevin empire was a collection of realms independent of one another, but with the same titular head.
Is it accurate to call France in 1066 'Francia'? I get the impression that that label was more appropriate to the earlier Carolingian period, and by 1066 it was just France.
Did this situation contribute to the Hundred Years War in later centuries?